1. Field of the Invention
The present invention relates to a random number generating element, and more particularly to a random number generating element that can be used to generate, for example, a cipher for protection of information.
2. Description of the Related Art
Pseudo-random numbers, which can be easily generated, are often used as random numbers needed to generate cipher keys for information security and protection. However, to realize higher security, it is necessary to use genuine random numbers to avoid a cipher being broken. To generate genuine random numbers, the natural phenomenon of random noise can be utilized.
In a certain random number generating element utilizing a physical phenomenon, random noise, such as thermal noise in a current flowing through a Schottky diode, is digitized to generate random numbers. More specifically, a Schottky diode current is filtered to eliminate part of its direct-current component, and then amplified to increase the ratio of the random noise component. The amplified random noise signal is oscillated by an oscillator circuit using a flip-flop. Fluctuations in the cycle of the random noise signal corresponding to those in the current are counted in synchronism with a clock signal of a higher frequency, and digitized, thereby generating a random number sequence. Since a physical phenomenon is utilized, random numbers close to genuine random numbers can be produced, which increases the security level, compared to the case of utilizing pseudo-random numbers.
On the other hand, the inventors of the present invention have developed a random number generating element capable of generating genuine random numbers utilizing electronic tunneling (see Jpn. Pat. Appln. KOKAI Publication No. 2003-108364).
To generate random numbers for information protection, a generation rate of 1 Mbit/s or more is required. However, in a random number generating element using random noise such as thermal noise mixed in a current flowing through a Schottky diode, only about 10−5% of the whole random noise component is a 1-MHz or more random noise component. Accordingly, an amplification of about 105 times is required, which may degrade the genuineness of the produced random numbers, or may significantly enlarge the entire apparatus because of the required amplifier circuit.